Choosing between Fault-Tolerance and Increased V&V
for Improving Reliability
The paper by Peter Popov, Lorenzo Strigini and Bev Littlewood was presented
at the International Conference on Parallel and Distributed Processing
Techniques and Applications (PDPTA'2000), June 26-29, 2000, Monte Carlo
Resort, Las Vegas, Nevada, USA), pp. 535-540, ISBN 1-892512-22-x, Copyright
CSREA Press. The full text is available as a .pdf
file. The abstract is given below.
Abstract
Fault tolerant systems based on the use of software design diversity
may be able to achieve high levels of reliability more cost-effectively
than other approaches, such as heroic debugging. Earlier experiments have
shown that multi-version software systems are more reliable than the individual
versions. However, it is also clear that the reliability benefits are much
worse than would be suggested by naive assumptions of failure independence
between the versions.
To decide whether to use design diversity or other means for achieving
the desired reliability a developer would need to know how they compare
from the viewpoint of cost-effectiveness. Empirical data are insufficient
for deciding this question, and expert opinions differ. We refute a recently
published argument in favour of diversity and in the process show some
general factors deciding whether process improvement, or debugging of the
versions in a multiple-version system, will increase or decrease the statistical
correlation between failures of the versions. The conclusion is that
there is as yet no evidence that the choice between design diversity and
other means of reliability improvement can be decided by general arguments
rather than by detailed (and uncertain) special-case analysis.
N-version design Versus one Good Version
The article by Bev Littlewood, Peter Popov and Lorenzo Strigini was
presented at the International Conference on Dependable Systems & Networks
(FTCS-30, DCCA-8), 24-27 June, 2000, New Your City, (USA). The text appears
in the 'Workshops and Fast abstracts' Digest of DSN'2000, pp. B42-B43.
The text is available for download as a .pdf
file.
Page maintained by: Peter Popov
Last modified 31 January 2000.